Pintle valves are well known for use in controlling flow of fluids, and especially gases. Some applications can expose a valve's internal surfaces and moving parts to fouling materials which can give rise to deposits, resulting in impaired action or outright failure of the valve. In a particularly severe application, exhaust gas recirculation pintle valves on internal combustion engines are known to accumulate coking deposits on the pintle shaft in the region of the pintle support bushing. Having this area of the pintle unobstructed is a requirement for smooth, reliable action of the valve in controlling exhaust gas flow.
It is known in the art to provide means for causing the pintle shaft to be scraped clean inherently by the axial motion of the shaft as the valve is exercised. Such means typically are disposed upstream of the sensitive area, such as a shaft bushing or a valve actuator.
U.S. Pat. No. 5,511,531, issued Apr. 30, 1996, discloses an annular scraper element 74 for the purpose of scraping off any residue that may accumulate on shaft 60 so that such residue is prevented from passing onto actuator 12. At its center, scraper element 74 has a circular hole with which shaft 60 has a close sliding fit. The radially outer margin of element 74 is captured such that it is constrained against any significant axial motion. A problem with such a scraper is that it represents essentially a line contact around the shaft, and any material that escapes past that line is then free to migrate or be deposited further along the shaft and/or within the actuator. Further, scraper element 74 has no radial resilience and is subject to wear with use, such that its scraping action becomes progressively less effective over time. Also, without radial resilience, any assembly axial misalignment between element 74 and shaft 60 could lead to erratic operation or binding of the shaft.
U.S. Pat. No. 4,253,642, issued Mar. 3, 1981, discloses an arrangement of wire bristles impinging radially on a rotational valve shaft “to clean threads or the like of the valve stem and remove debris therefrom.” A problem with using wire bristles is that, while the shaft may be scrubbed thereby, the bristle pattern is entirely porous, allowing particulate-laden gases to permeate through and cause coking downstream of the bristles. If the disclosed bristled device was used in an axially actuating valve, and no means for introducing radial resilience of the device was provided, erratic operation and binding of the shaft as discussed above could result.
U.S. Pat. No. 6,212,881 B1, issued Apr. 10, 2001, discloses a “stopper” 72 (FIG. 6) having a central hole 72b through which the valve pintle shaft 56a passes. The diameter of the hole 72b is slightly larger than the diameter of shaft 56a. When the valve shaft is moved axially, the inner surface of the hole removes foreign matter such as deposits from the surface of the valve shaft. This is substantially the same line-contact scraper mechanism as is disclosed in U.S. Pat. No. 5,511,531 discussed above and thus has the same drawbacks as discussed previously.
U.S. Pat. No. 5,666,932 discloses a programmed feature of an engine start-up cycle wherein the EGR valve is violently opened and then slammed closed, which purports to jar or shear any contaminant buildup so as to reduce such buildup. No contact means is disclosed for actively scraping or otherwise mechanically removing contaminant buildup.
U.S. Pat. No. 4,408,627, issued Oct. 11, 1983, discloses a gate-type EGR valve operated by a linear actuator attached to a valve shaft. A pair of nylon scraper rings 28,29 are positioned around the valve shaft “to remove any carbon deposits” from the valve shaft and prevent them from entering the actuator. The rings are separated by a compressed coil spring which urges the rings against respective axial sealing faces in the valve body. While some radial resilience of the scraper means may be provided, the scrapers remain subject to wear with use and degradation of effectiveness over time.
U.S. Pat. No. 4,061,157, issued Dec. 6, 1977, discloses a reciprocating valve having an outwardly facing conical surface disposed about the valve stem, which surface terminates in a knife-like edge that functions to remove accumulations of foreign material from exposed portions of the valve stem as it oscillates past the edge. The same inherent tendencies to bind or stick the stem if not properly aligned or to degrade over time exist in this design.
What is needed in the art is a means for keeping gas-borne contaminants from reaching bearing surfaces of a valve pintle shaft and its support bushing, and for limiting buildup of contaminants on a valve pintle shaft.
It is a principal object of the present invention to increase the reliability of an exhaust gas recirculation valve by preventing buildup of deposits on bearing surfaces thereof.